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• A Nb 4 N 5 micro-flower was developed to support IrO x as anode catalyst for PEMWE. • The IrO x /Nb 4 N 5 catalyst outperformed commercial IrO 2. • The catalyst-support interaction improved OER performance. • Superior performance and good stability were achieved for practical PEMWE operation. Precious metal Ir is still the best oxygen evolution reaction (OER) catalyst for polymer electrolyte membrane water electrolysis (PEMWE). Developing suitable support materials to improve the utilization rate of Ir is therefore of great significance for the practical application of PEMWE. Herein, we report a unique spherical Nb 4 N 5 µm-flower as an anode catalyst support for PEMWE. Through an organic colloidal method, a supported IrO x /Nb 4 N 5 catalyst was successfully prepared. TEM analysis showed that the IrO x particles were uniformly dispersed on the surface of the Nb 4 N 5 µm-flower, with a particle size of only about 1.8 nm. XPS revealed that Nb 4 N 5 can effectively regulate the d -band center of Ir, thereby reducing the adsorption energy between oxygen molecules and improving the OER efficiency. Half-cell tests and actual PEMWE operation demonstrate that the performance of the IrO x /Nb 4 N 5 catalyst is superior to commercial IrO 2. The overpotential was 247 mV at 10 mA cm−2, and the Tafel slope was only 53.2 mV dec−1 when the IrO 2 content was 40 wt %. Moreover, the mass activity was 857.6 A g –1 IrO2 at 1.7 V, which is 4.7 times that of commercial IrO 2. After an initial 150 h of PEMWE operation, the water decomposition voltage at 1 A cm−2 only increased by 5.5 %. These results suggest that the supported IrO x /Nb 4 N 5 catalyst is a promising candidate for real PEMWE applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Rational fabrication of an electrocatalyst with excellent stability, conductivity, and activity is urgently demanded for oxygen evolution reaction (OER). In this work, Ru-regulated hierarchical CoFe/CoFe 2 O 4 nanoparticles with graphitic carbon shells were successfully fabricated via self-assembling and vapor reduction strategies. Our investigation uncovers high concentrations of octahedral Co3+ sites in electrocatalysts can be triumphantly acquired via moderate Ru doping, which could give rise to excellent electrocatalytic activities during OER. In addition, the design of CoFe alloys and graphitic carbon shells can compensate for the weak conductivity of cobalt ferrites. Based on the intrinsic stability, improved conductivity and activity, the as-prepared electrocatalyst yields a low overpotential of 237 mV at 10 mA cm−2 and a small Tafel slope of 47 mV dec−1 in 1.0 M KOH electrolyte, exhibiting outstanding electrocatalytic activities for OER. This work effectually optimized the geometric sites of cations in spinel oxides via Ru introducing, and successfully enhanced conductivities of electrocatalysts by combining with CoFe alloys as well as graphitic carbon shells. [Display omitted] [ABSTRACT FROM AUTHOR]

Designing an efficient electrocatalyst for the oxygen evolution reaction (OER) in alkaline media is highly needed but very challenging task. Herein, we used organic polyelectrolytes such as (carboxymethyl cellulose) CMC and polyacrylamide polymers for the growth of Co 3 O 4 nanostructures by aqueous chemical growth method. The morphology and composition studies were performed on scanning electron microscopy (SEM), energy dispersive X-ray (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) techniques. The structural properties and the surface chemistry of the Co 3 O 4 electrocatalysts were correlated to the OER performance, and the enhancement mechanism with respect to pristine Co 3 O 4 was observed to be specifically related to the polyelectrolyte templating role. Co 3 O 4 @CMC composites displayed reduced crystallite size, producing OER overpotential as low as 290 mV at 10 mAcm−2 in 1.0 KOH and Tafel slope of 71 mVdec−1, suggesting fast transfer of intermediates and electrons during water electrolysis. On the other hand, the use of polyacrylamide and its different templating mechanism resulted in similar crystallite size, but preferential exposed faces and larger surface vacancies content, as demonstrated by HR-TEM and XPS, respectively. Consistently, this material displays cutting-edge OER performance, such as overpotential of 260 mV at 10 mAcm−2 and a low Tafel slope of 63 mVdec−1. The proposed strategy for the preparation of Co 3 O 4 nanostructures in the presence of CMC and polyacrylamide is facile, mass production, thus it could equally contributed towards the realization of hydrogen energy. Therefore, these nanostructures of Co 3 O 4 can be regarded as an alternative and promising materials for the different electrochemical applications including fuel cells, metal air batteries, overall water electrolysis and other energy storage devices. [ABSTRACT FROM AUTHOR]

Polymer electrolyte membrane water electrolysis (PEMWE) uses intermittent renewable energy and plays a key role in storing energy in the form of hydrogen. However, its widespread application is limited owing to issues associated with oxygen evolution reaction (OER) catalysts, including activity and stability. Thus, it is necessary to develop highly active and durable catalysts in this regard. Herein, an IrO x @IrO 2 catalyst with an ultrahigh surface area (G-450) was synthesized by a simple Adams fusion method and calcined at 450 °C with glycine as an additive. Owing to its micro/mesoporous structure, this catalyst exhibited an ultrahigh specific surface area (SSA) of 403 m2 g-1 and an amorphous structure with average oxidation states of Ir(IV). A trade-off between its OER activity and stability was achieved by controlling its SSA and Ir oxidation states via the optimization of the calcination temperature. Surface-rich Ir(III) species and high SSA enhanced the OER activity of G-450 (309 mV overpotential at 10 mA cm-2) compared with the IrO 2 catalyst prepared without glycine (A-450, 351 mV overpotential at 10 mA cm-2). Further, the G-450 exhibited an Ir dissolution rate that was 2.5-fold lower than that of the IrO 2 catalyst prepared at 350 °C (G-350) after 6 h chronopotentiometry at 10 mA cm-2, implying a higher stability owing to the presence of Ir(IV) species. Additionally, G-450 was introduced into the anode of the polymer electrolyte membrane (PEM) water electrolyzer single cell and demonstrated higher performance than A-450. The balanced activity and stability of IrO x @IrO 2 enhanced the PEM water electrolyzer performance. Moreover, this facile synthetic method is also applicable to the synthesis of binary oxide compounds and other transition metal oxides. [Display omitted] [ABSTRACT FROM AUTHOR]

• In situ growth method to prepare a binder-free IrO x -Ti (IT) anode with a very low IrO x loading amount is described. • The synthesized catalyst shows a high oxygen evolution reaction activity and durability in acidic media. • A flow-type polymer electrolyzer (polymer electrolyte alcohol electrosynthesis cell) that efficiently synthesized glycolic acid from oxalic acid is described. Alcohol is considered as a potential CO 2 -free energy carrier to replace hydrogen because of its high energy density, appropriate chemical stability and low-cost production. In this study, we describe the development of a simple in situ growth method to prepare a binder free IrO x -Ti anode with a very low IrO x loading amount (< 0.25 mg cm−2), and the obtained catalyst shows a high oxygen evolution reaction (OER) activity and durability in acidic media. The performance of a polymer electrolyte alcohol electrosynthesis cell (PEAEC) using this anode catalyst shows a better performance than that of PEAEC using a typical commercial IrO 2 -Ti paper anode with the loading of IrO 2 = 3 mg cm−2. Furthermore, the key factors that affect the performance of the PEAEC are determined by comparing the performances of the PEAEC with different anode catalysts. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Tri-electrode battery configurations using gel polymer electrolytes are studied. • Effects of crosslinking density on OER is evaluated. • Effects of ZnO on ORR and OER are revealed separately. • Cycling performance is shown in different orientations without leaking. To increase the cyclability of rechargeable zinc-air batteries (ZABs) using gel polymer electrolytes (GPEs), battery design and structure need to be optimized. Two different configurations for a tri-electrode battery have been developed in this work; i.e., a planar cell and a sandwich cell. Discharge-recharge cycling tests at 5 mA cm–2 show that the sandwich cell is more suitable for ZABs than the planar cell. Various additives for the GPEs, such as cross linking agents and ZnO, have also been evaluated using the tri-electrode design. Cross linking density affects the physical state of GPEs, which in turn affects the oxygen evolution reaction as there is an adverse effect of excessive GPE/Ni foam electrode contact area because oxygen bubbles may be trapped in the GPE. The addition of ZnO to the oxygen reduction reaction side of the battery enhances the cycling performance of ZABs; i.e., the battery can withstand at least 100 cycles at 5 mA cm–2 with an efficiency of 62% during the first cycle. Image, graphical abstract [ABSTRACT FROM AUTHOR]

For a typical Proton exchange membrane (PEM) water electrolysis system, reducing the amount of Ir loading at the anode in membrane electrode assembly (MEA), while maintaining the performance, is still a big challenge. Here, to improve the performance of catalyst layer for oxygen evolution reaction (OER) in an acidic medium, vertical aligned IrO x nanoarrays (IrO x NAs) were synthesized by electrodeposition with TiO 2 nanotube arrays (TNTA) as template. By tuning the scan rate in the electrodeposition process, IrO x open-end nanotube arrays with tunable length ranged from 500 nm to 1400 nm and hollow nanorod arrays were obtained due to a diffusion-controlled deposition process. By constructing 3-D electrode of 1-D catalyst with enhanced ion transfer, IrO x NAs performed almost the same current density of OER with 1/20 Ir loading amount compared with commercial IrO 2 nanoparticles, which could significantly reduce the cost of catalyst in PEM water electrolyser. Moreover, no apparent current decrease was observed even after 10 h' anodic polarization under 1.55 V, which exhibit excellent OER durability. [ABSTRACT FROM AUTHOR]